Noting that the world currently operates in an environment where the most dangerous weapon – the nuclear bomb – has only enhanced its standing as a ticket to "power, prestige, and an insurance policy" against foreign intervention, he adds, "We haven't done [well] at all."

But Mr. ElBaradei has a more optimistic view of future prospects, for two reasons related to the United States: the US today has a president who speaks seriously of getting to zero nuclear weapons, he says, and the US is now talking to Iran instead of ostracizing it.

He describes as "two very encouraging signs" the meetings that a high-level US diplomat and then Department of Energy officials held with Iranian counterparts in recent months. If the deal worked out with world powers for enriching much of Iran's low-enriched uranium stockpile outside of the country can be finalized – a deal Tehran has yet to accept – a door would open to a deemphasizing of nuclear weapons, he believes.

"If that would happen, that would be followed by a dialogue," he adds – on the nuclear issue, yes, but also on the regional security and development issues that he says are at the heart of the Iranian regime's concerns.

ElBaradei has been in New York this week, bidding farewell after 12 years during which he has taken an obscure, technical UN agency and elevated it, through charisma and deft diplomatic maneuvering, to the forefront of international diplomacy.

His success at giving the IAEA a profile few multilateral agencies enjoy is not all his own doing.

Over the period of his tenure, the issue of nuclear proliferation has been central to many of the major international crises, including North Korea, Iraq, Iran, and Pakistan, with the revelations of the A.Q. Khan nuclear technology bazaar.

Still, his expansion of the IAEA's profile into the political sphere has not always been appreciated. Former secretary of State Condoleezza Rice once accused him of "speaking outside his box" as head of a technical agency.

Mr. ElBaradei and the agency he administered for 12 years won the Nobel Peace Prize in 2005. The prize committee said its decision was based on IAEA efforts under ElBaradei to control the clandestine spread of nuclear materials, and for promoting safe, civilian uses of nuclear energy, particularly in the developing world.

Like this year's awarding of the Nobel Peace prize to President Obama, the ElBaradei prize was interpreted as a veiled criticism of former president Bush's use of ultimately baseless charges – that Saddam Hussein had weapons of mass destruction – to wage war on Iraq,

It is the case of Iraq, and the shortcomings of the international community revealed by that crisis, that seem to have marked ElBaradei most.

"I will always lament the fact that a tragic war was launched ... on the basis of a false pretext," he told the General Assembly. To help prevent the recurrence of such a "mistake," he says the IAEA should have broader powers – a stronger inspections regime, for example.

Ultimately, ElBaradei sees one answer to the world's nuclear insecurities in the creation of an international nuclear fuel supply system in which enrichment and reprocessing are "not a national prerogative but a multinational function," as he told his CFR audience.

Another requisite, he says, is that any international system overseeing the use of nuclear technology must be equitable in its bestowals. Zeroing in on what he sees as the root cause of the nuclear crises he witnessed, he says, "You can't have a system of haves and have-nots."